Active Surveillance (AS) is an increasingly adopted disease management approach for men diagnosed with low risk prostate cancer who meet very specific eligibility criteria. When combined with decisional ambiguity and concern regarding a choice to forgo active treatment to participate in AS, feelings of fear, uncertainty and a loss of control can arise. As a result, within 2-3 years of observation, some 25% of men who are clinically eligible for AS prematurely opt for definitive treatment. These rates can double by 5 years. Our team has conducted one of the only randomized controlled pilot studies of a therapeutic intervention called Mindfulness Based Stress Reduction (MBSR) to establish feasibility and preliminary efficacy of MBSR in assuaging AS-related psychosocial sequelae, such as fear of cancer progression and uncertainty, with men placed on AS and their spouses. OBJECTIVE: Examine the efficacy of MBSR with a larger, more culturally diverse, and geographically generalizable sample of men on AS and their spouses using a time and attention controlled matched condition. PRIMARY AIM: Examine Longitudinal Differences in Important, AS-Related Self- Reported Outcomes of Stress and Quality of Life Between Treatment and Control Groups Over Time. HYPOTHESIS I: MBSR group participants (n=120 men & 120 spouses) will experience significantly lower anxiety, fear of cancer progression, uncertainty intolerance, rumination, decisional regret, and higher treatment satisfaction, posttraumatic growth and global health related quality of life (HRQOL) compared to Health Promotion (n=120 men & 120 spouses). HYPOTHESIS II: Non-disease progression related attrition from AS will be associated with increased anxiety, fear of cancer progression, uncertainty intolerance, rumination, decisional regret, and lower treatment satisfaction, posttraumatic growth and global health related quality of life (HRQOL). HYPOTHESIS III: MBSR participants will display correspondingly higher rates of adherence to AS compared and Health Promotion participants. STUDY DESIGN: We will use a randomized, placebo-controlled, partially double-blinded study design to examine MBSR over 12 months (n=120 men on AS & 120 spouses), compared with a time matched control condition (n=120 men on AS & 120 spouses). Baseline measures will be obtained just prior to randomization to the three study arms (T1), followed by repeated assessments at 2 months (T2), 6 months (T3) and 12 months (T4). RELEVANCE: This work has the potential to offer men and their partners facing the stressors of AS with specialized emotional, cognitive, and physiological self-regulatory skills to cope more effectively and possibly prolong adherence to medically-warranted AS protocols.